Thermoplastic polymers, such as poly(aryl ketones), have a wide variety of uses in a number of engineering applications. Many thermoplastic polymers are well known engineering polymers, which can be made from a variety of starting materials. Poly(aryl ketones) have had the disadvantage, however, of being difficult to work with, for example, to form into a film or membrane. In particular, many poly(aryl ketones) do not dissolve readily in most solvents. Therefore, polymer solutions (or dopes) could not be formed or used as desired. Thus, films and membranes including poly(aryl ketones) could not be readily cast from solution.